This study concerns the cell biology of the retinal pigment epithelium in the RCS rat, an animal model of retinitis pigmentosa. The RCS rat retinal degeneration has been shown to be a defect in phagocytosis of the rod outer segments by the retinal pigment epithelium. Phagocytosis of isolated rod outer segments from diseased and control rats will be compared in tissue cultured retinal pigment epithelium from diseased and control rats. Congenic strains differing in only the retinal degeneration mutation will be used as the disease and control experimental animals. This in vitro investigation may eventually be extended to study the small amount of scarce material from human retinitis pigmentosa.